Reverse actuated pneumatic brake

Abstract

A pneumatic brake for a vehicle is provided. The pneumatic brake includes a housing and a single diaphragm within the housing that divides the housing into front and rear variable-volume chambers. A push rod is disposed in the front chamber and extends outwardly from the housing. A parking spring is disposed in the rear chamber and urges the diaphragm and push rod towards the front chamber. A valve body extends through the rear chamber and includes an elongated stem disposed in a telescoping relationship with the push rod. In resting and activation modes, brake pressure is applied by the parking spring to the top plate to activate a brake function. In a deactivation mode, pneumatic pressure is supplied to the front chamber to compress the parking spring and disengage the brake. A brake system including the pneumatic brake and an ABS is also provided.

The invention claimed is: 
     
       1. A pneumatic brake for a vehicle, the pneumatic brake providing a brake function and comprising:
 a cylindrical housing having a central, axially extending longitudinal axis; 
 a single diaphragm within the housing, the diaphragm dividing the housing into front and rear variable-volume chambers; 
 a push rod axially disposed along the central axis of the housing, the push rod having a proximate end and an opposite distal end, the proximate end being disposed in the front chamber and terminating in a top plate that is engaged with the diaphragm, the distal end extending outwardly from the housing; 
 a parking spring axially disposed in the rear chamber along the central axis of the housing, the parking spring urging the diaphragm against the top plate in a direction towards the front chamber; 
 a valve body extending axially through the rear chamber along the central axis of the housing, the valve body including an elongated stem coaxially aligned with the push rod, the stem extending into an opening in the top plate and being disposed in a telescoping relationship with the push rod; 
 a first supply passage in fluid communication with a valve port in the valve body; 
 the valve body including a passageway through the stem in fluid communication with the valve port, and the valve body further including a plurality of open and closeable transfer ports in fluid communication with the rear chamber; 
 the push rod including an internal chamber in fluid communication with the passageway in the valve body, the push rod further including a plurality of front chamber ports, the internal chamber of the push rod being in fluid communication with the front chamber via the plurality of front chamber ports; and 
 a second supply passage in fluid communication with the rear chamber via a plurality of rear chamber ports; 
 wherein in a resting mode with no pneumatic pressure in the front and rear chambers, brake pressure is applied by the parking spring to the top plate, in a deactivation mode pneumatic pressure is supplied to the front chamber to compress the parking spring and disengage the brake, and in an activation mode pneumatic pressure is transferred from the front chamber to the rear chamber, and pneumatic pressure is also supplied to the rear chamber via the second supply passage, to apply the brake function with both the pneumatic pressure and a spring force of the parking spring acting on the top plate. 
 
     
     
       2. The pneumatic brake of  claim 1 , further comprising an internal transfer valve disposed in the valve body, the internal transfer valve being movable within the valve body. 
     
     
       3. The pneumatic brake of  claim 2 , wherein the internal transfer valve has a generally tubular sidewall defining an internal passageway, a nose capping one end of the tubular sidewall, and an opposite open end. 
     
     
       4. The pneumatic brake of  claim 3 , wherein the internal transfer valve includes a plurality of supply ports in the sidewall adjacent the nose, the supply ports being in fluid communication with the passageway in the valve body. 
     
     
       5. The pneumatic brake of  claim 3 , wherein the nose of the internal transfer valve is receivable in the valve port in the valve body to close the valve port. 
     
     
       6. The pneumatic brake of  claim 3 , wherein the sidewall of the internal transfer valve includes a stepped portion, and the valve body includes an internal shoulder that defines a stop for the stepped portion of the internal transfer valve. 
     
     
       7. The pneumatic brake of  claim 6 , further comprising a valve spring disposed within the internal passageway of the internal transfer valve, the stepped portion of the sidewall defining a spring seat, the valve spring being in urged engagement with the spring seat and the internal shoulder of the valve body. 
     
     
       8. The pneumatic brake of  claim 2 , wherein sliding movement of the internal transfer valve in the valve body opens and closes the transfer ports. 
     
     
       9. The pneumatic brake of  claim 2 , wherein the valve body includes a plurality of balance ports in fluid communication with the rear chamber, the sidewall of the internal transfer valve includes a stepped portion, and the internal transfer valve further includes an annular protrusion extending outwardly from the sidewall, the stepped portion and the annular protrusion contacting an inner surface of the valve body, wherein a balance chamber is defined by the stepped portion, the annular protrusion, the sidewall of the internal transfer valve between the stepped portion and the annular protrusion, and the inner surface of the valve body, the balance chamber being in fluid communication with the rear chamber via the balance ports. 
     
     
       10. The pneumatic brake of  claim 1 , wherein the valve body is continuous with the first supply passage, the first supply passage is coaxially disposed within the second supply passage, and a portion of the second supply passage surrounds the first supply passage. 
     
     
       11. The pneumatic brake of  claim 1 , wherein the second supply passage is defined in part by a swivel fitting that is fitted within an opening in the rear chamber of the housing. 
     
     
       12. The pneumatic brake of  claim 1 , wherein the spring force of the parking spring is equivalent to a pneumatic pressure in the range of 50 to 70 psi. 
     
     
       13. The pneumatic brake of  claim 1 , further including a two-position spool valve in fluid communication with the first supply passage and the second supply passage. 
     
     
       14. The pneumatic brake of  claim 13 , wherein the spool valve is a 4/2 proportional valve. 
     
     
       15. A brake system including the pneumatic brake of  claim 1  connected to an anti-lock braking system (ABS). 
     
     
       16. The brake system of  claim 15 , wherein the first and second supply passages are connected through the ABS to a source of pneumatic pressure in the range of 110 to 130 psi. 
     
     
       17. The brake system of  claim 15 , wherein the first and second supply passages are vented to atmosphere through the ABS.